KR100460980B1 - Apparatus and method for improvement of printing image quality - Google Patents

Abstract

An apparatus and method for improving print quality are disclosed. An apparatus for improving the print quality of a document having a mixed background, text, and picture includes: a pixel division unit for dividing a pixel of interest in image data obtained by scanning a mixed document into one of a text pixel, a background pixel, and a picture pixel and outputting the pixel; And a contrast correction unit for adaptively selecting a plurality of preset brightness equalization patterns according to the characteristics of the pixels of interest divided by the pixel separator to correct the brightness levels of the pixels of interest. As a result, the contrast of the input pixel can be improved, and the print quality of the document in which the background, characters, and pictures are mixed can be improved.

Description

Apparatus and method for improvement of printing image quality}

The present invention relates to an apparatus for improving a print quality. More particularly, the contrast is adaptively adjusted according to the characteristics of each input pixel in a mixed document in which text and image are mixed. The present invention relates to an apparatus for improving a print quality that can be corrected.

Image processing apparatuses such as an image scanner, facsimile, and digital copier are provided with an apparatus for improving print quality. The print quality improving apparatus improves the print quality through image quality improvement algorithms such as outline enhancement and contrast correction to improve the print quality of the document to be printed.

In general, as a method for contrast correction, gamma correction and histogram equalization according to a change in brightness may be mentioned. Here, the histogram equalization has the effect of stretching the dynamic range, thereby flattening the gray distribution of the resulting image, and as a result, improving the contrast of the image.

In the conventional print quality improving apparatus, when the contrast is corrected to improve the print quality, the brightness is uniformly corrected by applying one brightness equalization pattern regardless of the characteristics of the data to be printed. In the case of mixed documents with mixed data of different characteristics such as background, text, graphics, and photographs, if the correction is made by applying one brightness equalization pattern, the print quality may be reduced due to the inherent characteristics of each data. A problem occurs.

The technical problem to be achieved by the present invention is to divide the input pixel into a text, a background, or a picture pixel for a document having a mixture of characters and pictures, and to improve the image quality by adaptively correcting the contrast according to the characteristics of the divided input pixels. It is to provide a print quality improving apparatus and a method thereof.

1 is a block diagram of an apparatus for improving a print quality according to a preferred embodiment of the present invention;

2A to 2C are diagrams showing an example of brightness equalization patterns according to characteristics of the pixel of interest; and

3 is a flowchart illustrating a method of improving image quality of the apparatus for improving a print quality shown in FIG. 1.

Explanation of symbols on the main parts of the drawings

100: print quality improvement device 110: color conversion processing unit

120: pixel segmentation unit 130: contrast correction unit

140: print processing unit 150: history information storage unit

160: region division

In order to solve the above technical problem, an apparatus for improving the print quality of a document having a mixed background, text, and picture according to the present invention includes a text pixel, a background of a pixel of interest in image data obtained by scanning the document. The brightness level of the pixel of interest by adaptively selecting a predetermined brightness equalization pattern according to the characteristics of the pixel segmentation unit and the pixel of division of the pixel divided by one of a pixel and a picture pixel Contrast correction unit for correcting the.

Preferably, an area division unit for dividing the pixel of interest divided into any one of the character pixel, the background pixel, and the picture pixel by the pixel division unit into any one of a character area, a background area, and a picture area is further included. Equipped. In this case, the contrast correction unit corrects the brightness level of the pixel of interest using the brightness equalization pattern different for each of the regions.

In addition, when the image data obtained by scanning the document is color data, a color conversion processing unit for converting the color data into lightness / saturation data having a lightness component and a saturation component, and further outputs, the pixel separation unit The pixel of interest is classified into one of the text pixel, the background pixel, and the picture pixel based on the brightness / saturation data.

The contrast correction unit uses the brightness equalization pattern in which the brightness / saturation data is classified into at least two classes based on a predetermined brightness threshold among the plurality of brightness equalization patterns. It is preferable to correct the brightness level of the pixel of interest.

The contrast correction unit processes the text pixel as white for pixels whose brightness level of the pixel of interest is greater than or equal to the brightness threshold, and processes the text pixel as black for pixels that are less than or equal to the brightness threshold.

In addition, the contrast correction unit may include brightness equalization in which the brightness / saturation data is classified into three or more brightness classes based on two or more brightness thresholds of the plurality of brightness equalization patterns. The brightness level of the pixel of interest is corrected using a pattern.

On the other hand, in order to solve the above technical problem, the method for improving the print quality of the document mixed with the background, characters and pictures according to the present invention, the pixel of interest of the image data obtained by scanning the document Correcting the brightness level of the pixel of interest by adaptively selecting a plurality of preset brightness equalization patterns according to the characteristics of the pixel of interest classified in the pixel division step and outputting the image into one of a background pixel and a picture pixel; It includes a step.

Preferably, the method further comprises converting the color data into brightness / saturation data having a brightness component and a saturation component when the image data obtained by scanning the document is color data, and outputting the color data. Divides the pixel of interest into one of the background pixel, the text pixel, and the picture pixel based on the brightness / saturation data.

In the correcting step, the brightness level of the pixel of interest is determined by using a brightness equalization pattern in which the brightness / saturation data is classified into at least two classes based on a predetermined brightness threshold for the pixel of interest that is divided into the character pixels. Calibrate

In the correcting step, for the pixel of interest divided into the picture pixels, the brightness equalization in which the brightness / saturation data is classified into three or more brightness classes based on two or more brightness thresholds of the plurality of brightness equalization patterns. The brightness level of the pixel of interest is corrected using a pattern.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a block diagram of a print quality improving apparatus according to a preferred embodiment of the present invention.

Referring to FIG. 1, the print quality improving apparatus 100 includes a color conversion processing unit 110, a pixel separation unit 120, a contrast correction unit 130, and a print processing unit 140.

The print quality improvement apparatus 100 according to the present invention improves the image quality by correcting the contrast of image data composed of pixels having a predetermined resolution obtained by scanning from an image reading apparatus such as a scanner (not shown).

If the document to be printed is a color document, the color conversion processing unit 110 converts the RGB color data of the pixel of interest to color data having a brightness component and a saturation component.

Models representing colors are classified by classifying colors according to their attributes, such as hue, saturation, chroma, brightness, and brightness. Used to specify

Color models include RGB (Red, Green, Blue) models for color monitors and color video cameras, and YIQ models and YCbCr models, which are standard for color television broadcasting.

The RGB color model is derived from the way the camera or scanner's image sensor and display light emitting device operate. In order to process a 256-color color image, 8 bits are allocated to each of R, G, and B per pixel, and thus 3 bytes of storage space are required for each pixel.

The YIQ color model is adopted for compatibility with equipment used in color television broadcasting, and it separates RGB color data into brightness and saturation components. The Y (luminance) component representing brightness provides all the video information required by a black and white television, and the I and Q components representing saturation are color components representing in-phase and quadrature, respectively.

The YCbCr color model is another color space that separates brightness from color information. Here, Y represents brightness, Cb represents a blue color difference signal, and Cr represents a red color difference signal. Compared to the RGB signals having the same bandwidth, the CbCr color difference signal of the YCbCr signal is effectively used because the bandwidth is reduced.

The color conversion processing unit 110 converts color data using any one of the color models described above. The brightness / saturation data output through the color conversion processor 110 is transmitted to the pixel separation unit 120. On the other hand, when the print target data is gray data (gray_data), the color conversion process is not performed, and the gray data is directly input to the pixel separator 120.

The pixel dividing unit 120 converts a target pixel into a text pixel, a background pixel, or an image pixel based on the brightness / saturation data output from the color conversion processing unit 110. Separate by. The pixel of interest refers to a pixel to be distinguished in order to perform contrast correction according to the present invention.

The pixel dividing unit 120 converts the pixel of interest to a pixel pixel, a background pixel, or a picture pixel using a brightness threshold and a saturation threshold preset for the brightness component and the chroma component separated by the color conversion processing unit 110. Separate by. Preferably, the pixel of interest is divided into a character pixel, a background pixel, or a picture pixel using a predetermined high brightness threshold th0 and a low brightness threshold th1. Since the pixel classification method is disclosed in Patent Application No. P2002-0044489 previously filed by the same applicant, detailed description thereof will be omitted.

The contrast corrector 130 adaptively selects a plurality of preset brightness equalization patterns according to the characteristics of the pixels of interest divided by the pixel separator 120 to correct the brightness levels of the pixels of interest.

2A to 2C are diagrams showing an example of brightness equalization patterns according to characteristics of a pixel of interest.

Referring to the drawings, x is the brightness level of the pixel of interest input to the contrast correction unit 130, f (x1, x2, x3) is a brightness equalization pattern for generating a brightness equalization value for x, LUT (x) is It represents the brightness equalization value of x.

The brightness equalization pattern is a transfer function for generating a brightness level of the output pixel corresponding to the input brightness level of the pixel of interest, that is, a brightness equalization value. The brightness equalization pattern is pre-stored in a look-up table (LUT) 132 of the contrast correction unit 130.

The contrast correction unit 130 corrects the brightness level of the pixel of interest by adaptively selecting a plurality of brightness equalization patterns previously stored in the LUT 132 according to the pixel of interest divided into a text pixel, a background pixel, or a picture pixel.

For example, the contrast correction unit 130 uses the brightness equalization pattern f (x1) as shown in FIG. 2A for the pixel of interest divided by the pixel division unit 120 into the pixel of interest. Correct the level. As shown in Fig. 2A, the brightness equalization pattern f (x1) of the character pixel classifies the brightness level of the pixel of interest into two classes based on a predetermined brightness threshold value. Pixels greater than or equal to the threshold value perform white filling, and black filling is performed to completely black the pixel whose brightness level of the input pixel of interest is equal to or less than the brightness threshold.

For example, in the case of the color 256-gradation output, the contrast correction unit 130 specifies R = 255, G = 255, and B = 255 for pixels whose brightness level of the pixel of interest is equal to or higher than the brightness threshold. On the other hand, the contrast correction unit 130 specifies R = 0, G = 0, and B = 0 by performing black fill on pixels having the brightness level of the pixel of interest equal to or less than the brightness threshold.

On the other hand, the picture pixel output from the pixel segmentation unit 120 includes a graphic pixel and a photograph pixel.

The contrast correction unit 130 corrects the brightness levels of the graphics pixels using the brightness equalization pattern f (x2) as shown in FIG. 2B for the pixels of interest divided into graphics pixels. The brightness equalization pattern f (x2) for correcting the brightness level of the graphics pixel is determined by adjusting the brightness level of the pixel of interest to three brightness classes based on two brightness thresholds (x1 and x2) as shown in FIG. 2B. Classify. The contrast correction unit 130 adaptively selects three brightness classes according to the input brightness levels of the pixel of interest and corrects the brightness levels of the graphic pixels. The brightness equalization pattern f (x2) of the graphics pixel is for increasing the contrast effect. In the case of graphic pixels, brightness is expressed using a few gray scales out of 256 gray scales, and thus the sharpness of the graphic pixels can be increased by increasing the contrast effect.

In addition, the contrast correction unit 130 corrects the brightness level of the photo pixel using the brightness equalization pattern f (x3) as shown in FIG. 2C for the pixel of interest divided into the photo pixel. The brightness equalization pattern f (x3) for correcting the brightness levels of the photo pixels is similar to the brightness equalization pattern f (x (2)) of the graphic pixels, and the brightness levels of the pixel of interest are set to two brightness thresholds (x1, x2). 3) Brightness equalization pattern (f (x3)), which has a weaker contrast effect than graphic pixels, is preferable. Therefore, it is desirable to increase the contrast effect so that it may look like an artificially processed image.

For the pixels of interest separated by the background pixels, the contrast correction unit 130 performs white filling to be processed as a full white so that the brightness level of the output pixel is set to 255 in the case of color 256 gray scale output. do.

Meanwhile, the contrast correction may be performed by varying the brightness equalization pattern for each region to which a character pixel, a background pixel, or a picture pixel belongs, without performing contrast correction for each pixel divided by the pixel dividing unit 120.

In this case, the print quality improving apparatus 100 may further include a history information storing unit 150 and an area separating unit 160.

The history information storage unit 150 stores the number of pixels of the same kind consecutive from the pixel separator 120 as the background history information or the picture history information. The history information storage unit 150 counts the number of consecutive background pixels before the pixel of interest based on the pixel separation signal output from the pixel separator 120, and stores the number of background pixels as background history information at a predetermined address corresponding to the pixel of interest. do. In addition, the history information storage unit 150 counts the number of consecutive picture pixels and stores them as picture history information at a predetermined address corresponding to the pixel of interest.

The area separator 160 receives the background history information or the picture history information corresponding to the pixel of interest from the history information storage unit 150 and divides the pixel of interest into a text area, a background area, or a picture area.

Since the history information storage method and the area classification method are disclosed in the patent application number P2002-0044489 previously filed by the same applicant, a detailed description thereof will be omitted. On the other hand, the pixel classification method and the area classification method is not limited to this, but it is a matter of course that both the pixel and the method of distinguishing the area to which the pixel belongs can be applied.

The contrast correction unit 130 is similar to correcting the brightness level of the pixel of interest by using different brightness equalization patterns for each divided pixel, and also applies to the character area, the background area, or the picture area divided by the area separator 160. The brightness level of the pixel of interest is corrected using a brightness equalization pattern suitable for each region.

The print processor 140 may include color correction for correcting the data output through the contrast correction unit 130 to a color suitable for a printer (not shown), and scaling for changing the print target data to match the size of the recording paper. scaling and halftoning for binarizing the print target data into 0 or 1 data. The data output_data signaled by the print processor 140 is transmitted to a print engine (not shown) and printed.

Hereinafter, a method of improving image quality of a print quality improving apparatus according to an exemplary embodiment of the present invention will be described with reference to FIG. 3.

First, the apparatus 100 for improving image quality determines whether image data including pixels having a predetermined resolution obtained by scanning a document containing a mixture of text, a background, and a picture is color data (color_data) or gray data (gray_data). (S200).

When the image data is the color data in step S200, the color conversion processing unit 110 converts the RGB color data of the pixel of interest into brightness / saturation data having a brightness component and a saturation component and outputs it (S210). If image data is determined to be gray data in step S200, step S210 is not performed. That is, step S220 is performed immediately after step S200.

The pixel dividing unit 120 divides the pixel of interest into one of a background pixel, a text pixel, and a picture pixel by using the brightness / saturation data input from the color conversion processing unit 110 and outputs a result of the division ( S220). Here, the picture pixels are divided into graphic pixels and photo pixels.

When the pixel division signal for the pixel of interest is received from the pixel division unit 120, the contrast correction unit 130 corrects the brightness level of the input pixel by using the brightness equalization pattern different for each divided pixel (S230).

In this case, when the pixel of interest is divided into a background pixel, the contrast correction unit 130 corrects the brightness level of the background pixel by performing white filling processing as a complete white. For example, in the case of the color 256-gradation output, the brightness level of the background pixel is set to 255.

When the pixel of interest is divided into text pixels, the contrast correction unit 130 corrects the brightness level of the text pixels using the brightness equalization pattern f (x1) as shown in FIG. 2A. That is, white filling is performed for pixels whose brightness level is greater than or equal to the brightness threshold, and black filling is performed for pixels less than or equal to the brightness threshold.

For the pixels of interest divided into graphic pixels by the pixel dividing unit 120, the contrast correction unit 130 may include the brightness equalization pattern (as shown in FIG. 2B) among the plurality of brightness equalization patterns stored in the LUT 132. f (x2)) is used to correct the brightness level of the graphics pixel.

On the other hand, with respect to the pixel of interest divided into the picture pixels by the pixel dividing unit 120, the contrast correction unit 130 of the plurality of brightness equalization patterns stored in the LUT 132 (as shown in FIG. f (x3)) is used to correct the brightness level of the picture pixel.

Finally, the print quality improvement apparatus 100 determines whether the pixel of interest currently input is the last pixel to be contrast corrected (S240). In step S240, if it is determined that the pixel of interest is the final pixel, the contrast correction process is terminated. The above-described steps S200 to S230 are contrast correction processes for one pixel of interest. Therefore, step S240 is a step provided to perform a contrast correction process on one pixel of interest, and to perform a contrast correction process on all pixels scanned and input in the same manner with the next adjacent pixel as the center of attention.

On the other hand, as described above, in addition to correcting the contrast for each pixel divided by the pixel dividing unit 120, the brightness for the input pixel may be corrected by adaptively selecting a brightness equalization pattern for each region to which the divided pixel belongs. Of course it can be implemented to be.

Although the present invention has been described in detail through the representative embodiments, those skilled in the art to which the present invention pertains can make various modifications without departing from the scope of the present invention. Will understand. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims below and equivalents thereof.

As described so far, according to the apparatus and method for improving a print quality according to the present invention, a pixel input corresponding to a document in which a background, a character, and a picture are mixed is divided into a character pixel, a background pixel, or a picture pixel, and classified. The contrast of the input pixels can be improved by adaptively selecting a plurality of preset brightness equalization patterns according to the pixels, and correcting the brightness levels of the input pixels. As a result, the print quality of the document in which the background, text and pictures are mixed can be improved.

Claims (10)

An apparatus for improving the print quality of a document in which backgrounds, characters, and pictures are mixed, A pixel division unit for dividing a pixel of interest of image data obtained by scanning the document into any one of a text pixel, a background pixel, and a picture pixel; And And a contrast correction unit for adaptively selecting a plurality of predetermined brightness equalization patterns according to the characteristics of the pixel of interest divided by the pixel separator to correct the brightness level of the pixel of interest. Image quality improvement device. The method of claim 1, And a region dividing unit configured to divide the pixel of interest divided into any one of the text pixel, the background pixel, and the drawing pixel into any one of a text area, a background area, and a picture area by the pixel separator. , And the contrast correction unit corrects the brightness level of the pixel of interest by using the brightness equalization pattern different for each of the regions. The method of claim 1, If the image data obtained by scanning the document is color data, a color conversion processing unit for converting the color data into brightness / saturation data having a brightness component and a saturation component and outputs; And the pixel dividing unit divides the pixel of interest into one of the text pixel, the background pixel, and the picture pixel based on the brightness / saturation data. The method of claim 3, wherein The contrast correction unit uses the brightness equalization pattern in which the brightness / saturation data is classified into at least two classes based on a predetermined brightness threshold among the plurality of brightness equalization patterns. And a brightness level of the pixel of interest. The method of claim 4, wherein And the contrast correction unit processes the text pixel as white for pixels whose brightness level of the pixel of interest is greater than or equal to the brightness threshold, and processes the text pixel as black for pixels that are less than or equal to the brightness threshold. Image quality improvement device. The method of claim 1, The contrast corrector may include a brightness equalization pattern in which the brightness / saturation data is classified into three or more brightness classes based on two or more brightness thresholds of the plurality of brightness equalization patterns. And the brightness level of the pixel of interest is corrected. In the method for improving the print quality of a document with mixed background, text and pictures, Dividing the pixel of interest of the image data obtained by scanning the document into any one of a text pixel, a background pixel, and a picture pixel; And And adaptively selecting a plurality of predetermined brightness equalization patterns according to the characteristics of the pixel of interest separated in the pixel discrimination step to correct brightness levels of the pixel of interest. The method of claim 7, wherein If the image data obtained by scanning the document is color data, converting the color data into brightness / saturation data having a brightness component and a saturation component, and outputting the converted color data; And dividing the pixel of interest into one of the background pixel, the character pixel, and the picture pixel based on the brightness / saturation data. The method of claim 8, In the correcting step, the brightness level of the pixel of interest is determined by using a brightness equalization pattern in which the brightness / saturation data is classified into at least two classes based on a predetermined brightness threshold for the pixel of interest that is divided into the character pixels. How to improve the print quality, characterized in that for correcting. The method of claim 8, In the correcting step, for the pixel of interest divided into the picture pixels, a brightness equalization pattern in which the brightness / saturation data is classified into three or more brightness classes based on two or more brightness thresholds among the plurality of brightness equalization patterns. And correcting the brightness level of the pixel of interest.